Tools for diagnosing "Check Engine Soon" light?

2000 Mistubishi Galant ES V6.
Check Engine Soon light came on a week ago, the morning after an 1,800
mile trip over five days. No problems during the trip.

Background: 60,000 mile servicing was done at the dealer about five
months ago. Since then I've had new tires, rear-brakes and an oil
change.
What I'd like to do is start working on the car myself from here on
out rather than going to the dealer all the time, and was wondering if
this would be a good time to get a device that would read the ECU and
tell me what the problem might be.
Questions - which brand/models should I look at? I've seen some
devices in Sears for about $100-$200 that will read the codes.
Wondering if those are good, or if I should look elsewhere?
Thanks for any tips.
Himanshu

Well simpleton is right, how detailed do you want to get. Cheapest unit
I've seen is $39.00USD, most expensive, $3000.00USD plus.
The first 1000 code definitions are available on the net, any auto parts
shop will tell you what the code is, usually free. This would be
inconvenient if your trouble shooting a repair, (after you changed something
does the code clear or change).
The Sears unit logs about 75 hours (300 hours on the deluxe unit), it stores
the data, then you play it back on your PC. Good for monitoring, but I
don't like the idea of having to plug the unit into your pc to read it,
that'll be a pain if your doing repairs and want to know the progress of
those repairs (back and forth to your PC). Might be great to monitor your
teens vehicle abusage (usage). Made for Sears by Davis Instruments
http://www.thecarchip.com /
Harbour freight sells one that only displays the error code, $39.00 I think,
and they give you a list of the first 1000 error codes (there are more than
1000 codes). This one is real simple. The unit displays a number, you then
look up the number on a supplied chart, for the description.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumberF030
B and B Electronics sells one that lets you program multiple readings on
your PC(or laptop), and they do it in real time, so you can drive your car
and watch the different readings change on your laptop, as it reads the
ECU's parameters (RPM, water temp, oil temp, O2, etc). It even stores the
data so you can see what the engine was doing just before you hit that tree
cause you were watching the laptop and not where you were driving. They
also offer a PDA version.
http://www.obdii.com/obdii.html
One thing I've notice though, is that except for the clear "service engine
soon light", very few give you the option of "controlling" the ECU, such as
putting it in diag mode, or forcing the ECU to test certain devices.
For these functions your into the $1000 range.
There is a company in Canada, that will sell you the decode chip, so you can
build your own interface between the car and the PC, about $20.00, I think.
Another company will sell you the PCB for that chip.
http://www.elmelectronics.com /
Depends what you want I guess.
My car is still under warranty for two more years, then I'm thinking of the
B and B unit, as my personal choice.
OBTW, by US law, the first 1000 codes must be the same for all car
manufacturers. The next group, beyond 1000 is available to each
manufacturer, for what ever they want. Usually a service manual will have
the vendor specific codes (my Eclipse manual does). When researching your
Scan Tool, check to see that it can display at least the numeric value of
codes above 1000, then you can look them up in your service manual.
In some cases, such as for some, Ford, GM, and Chrysler products, the vendor
has the specific codes programmed into the Scan Tool, but for Asian and
European, probably not.
OBTW again, Scantools may or may not be interchangeable between
manufacturers. The interface voltage may be different.
More sites;
http://www.softwareforcars.com/AeroCart/list.asp?cat=2,14,19,50,0
Do a goole search for OBD2 and "Scantool"

I came in late in this discussion. I do have an inexpensive
(AutoXray) OBll reader that I use for my Infiniti QX4 2003. There is
no module or adapter for my 1991 3000GTSL (60,000 miles).
Is there any relatively inexpensive way to read the codes on the
3000GTSL?
Norm
wrote:

Great! I didn't know that. AutoZone looked at it and found that it
was code P0155, which translates to "O2 Sensor Heater Circuit
Malfunction (Bank 2, Sensor 1)". Apparently there were two of the
same codes stored in memory.
There was some confusion at the store because the parts system asked
not only if it was before or after the catalytic converter, but also
if it was in front of the exhaust manifold (near the radiator), or
behind it (near the firewall). The AutoZoners were a bit muddled, but
finally said that Bank 2 means "after the cat. converter", and Sensor
1 was "in the front (radiator)" -- is that correct?
For this car (Mitsu Galant 2000 ES V6, California emission), a Bosch
O2 sensor is $173. I'm not sure of how easy it is to install it...I
looked for a Haynes/Chilton manual but the local stores didn't seem to
have one in stock for this model.
After the O2 sensor is replaced, will the "Service Engine Soon" light
go away, or does it need to be reset? Any experiences on replacing
the O2 sensor appreciated.
Finally, the car is still under extended warranty as I found out
yesterday by rummaging through my papers. Is the O2 sensor something
that would be covered under that, or is this more of a brakes-n-tires
kind of replacement?
Thanks.
Himanshu

Replacing the O2 sensor is fairly easy as long as you can get good access to
it. Basically you unplug it, using a wrench unscrew it. Replace with new in
reverse order. An adjustable wrench should work fine.
I'd call the warranty company and ask if they cover o2 sensor failure.
AutoZone can clear the code from the computer for you.
BTW, just because the heater circuit is showing bad, it doesn't mean the
sensor is at fault. Modern O2 sensors have a heater element in them, so
they work sooner and don't have to rely on heat from the exhaust to make
them work. What I'm saying is you may replace the O2 sensor and still have
a problem. There could be a bad connection somewhere.
You should really test the sensor instead of just replacing it. The
factory service manual should describe the correct procedure for this. I
don't have a copy of a manual handy to help you there.
I'd probably go and replace the sensor myself, but be prepared for it not to
solve the problem.
Without a real factory service manual (They are expensive) there's not much
you can do except change parts until you fix the problem unless you take the
car somewhere.
Rich

Autozone can clear it for you. My 01 Firebird TA set a similar code for
a failed 02 sensor - I cleared it before buying a replacement sensor -
that was 2 months ago... light hasn't come back on. My scantool I
bought sits unused...
I looked in the shop manual for my car and (for mine anyway but I think
it might be an OBD-2 emissions thing) the sensor has to fail twice
before the light comes on, which explains the 2 failures. If it then
passes diagnostics for 40 (IIRC) warmup cycles the light will go off.
So, before you spend $$$ on a new sensor, clear the code. Drive for a
couple of days - if it comes back, you need a new sensor. If not,
you're good to go until it does fail (which could be 2 days or 10 years
from now...)
And it probably won't be covered under an extended warranty - most ones
I've seen consider it to be like brake pads - a consumable.
Ray

That's $173 *each time you have to replace it*. Save yourself the costs
and aggravation...don't use the Bosch O2 sensors sold through AutoZone/Pep
Boys/Kragen type places, they are *junk*.
NTK , NAPA Echlin, Standard-BlueStreak, Dana...all dandy.

Before you buy that sensor, I'd buy a digital voltmeter (a cheap one) and
test the O2 sensor to see if it and it's heater are functioning.
On a 2003 V6 Mitsu engine, without VIC, the service manual shows 4 (four)
oxygen sensors.
Right bank front, heater wires colour codes are red (+12)and blue-white
tracer (grd)
O2 sensor, blue (grd) and green (signal)
Right bank rear, heater wires colour code are, red (+12) and brown (grd)
O2 sensor, pink (grd) and blue (signal)
Left bank front, heater wires colour codes are red (+12)and brown-white
tracer (grd).
O2 sensor, black (grd) and white (signal)
Left bank rear, heater wires colour code are, red (+12) and blue
white-tracer (grd).
O2 sensor, blue (grd) and yellow (signal)
BEWARE, this is for a 2003 V6 engine, should be the same as yours, but you
never know. Check your local library, some times they have service manuals
you can read through.
The heater is powered through the MFI relay, so your cars ignition will need
to be in the "run" position to measure the voltage.
With the engine at operating temperature try this, you can test the O2
signal.
The "signal" from the O2 sensor is a small voltage between .1 and .9 volts,
and it should vary between these levels frequently. The manual states "
While repeatedly revving the engine, measure the heated oxygen sensor output
voltage"" it should be between 0.6 and 1.0 volts". If the sensor doesn't
produce this voltage, it is most likely defective. You have three others to
compare with.
The heater has a resistance (also measurable with the digital voltmeter) of
between;
Right bank, left bank rear,11 and 18 ohms at 20 degrees C,
Right bank, left bank front,4.5 and 8 ohms at 20 degrees C.
Remember, this is for a 2003 V6.
The O2 sensor must be connected to the harness to measure the signal. Use
small pins to pierce the insulation to attach your voltmeter.

Thanks for the details. In the 2000 Galant 3.0 V6 (I believe it's a
6G72 engine) - I poked around yesterday to find only three O2 sensors.
I took some pictures that will be available temporarily at this URL
<http://home.comcast.net/~hgohel/index.html
Depending on your browser you might have to scroll horizontally or
vertically to see three shots:
1. O2 Sensor Firewall Side (red rectangle around it)
2. O2 Sensor Radiator Side (yellow rectangle around it)
3. O2 Sensor Cat. Conv - this is vertically below the radiator side
sensor.
I'm not sure if the third sensor is the pre-cat or post-cat? If there
are three sensors, is #2 the pre-cat and #3 the post-cat?
I really think that there might be four O2 sensors, and that I haven't
found the location of the fourth one yet.
Basically I need to identify "Bank 2, Sensor 1" according to the code
P0155, which at the moment I'm guessing is the one I've shown as #2 -
radiator side.
Thanks once again.
Himanshu

Well, your guess is as good as mine. I looked thought the service manual
(2003, 6G72 engine)for the O2 location as described by the error code, but
couldn't find it.
And you do have four O2 sensors. You have three cats , it appears that the
O2 sensors are on either side of the cats, attached to the exhaust manifold.
The P0155 code is a generic description of the fault.
You might have to test each O2 sensor till you find one with an open heater.

Many of them are. Realize that the ones that Bosch sells to automakers are
*not* the same ones they box up and sell to consumer-level auto parts
stores. The problem isn't universal across the Bosch aftermarket O2 sensor
line, but it is a fairly widespread phenomenon that a Bosch aftermarket O2
sensor will fail early and require replacement again. I have seen it cause
a great deal of headscratching and tailchasing ("It *can't* be the O2
Sensor, I just replaced it!").
Anyway, there's no reason to buy a dubious Bosch aftermarket sensor when
consistently-better ones are available from so many other manufacturers.

Thank you all for the fantastic replies; I'm much more informed than I was
yesterday!
So to answer some of the queries:
- Bumper-to-bumper warranty on this car is over. I believe it was 3
year/36,000 mile
- Extended warranty is 72,000 miles or 72 months, whichver is sooner. This
is still active. Called the warranty company and atleast on the phone they
said O2 sensor would not be covered. Will read through the paperwork to see
if I can find any more info
- Dealer wants minimum $39 to look at car & scan the code, but I'll check
with them about the federal emissions requirement/coverage as someone
mentioned. However, since I have 68,000 miles (4th year) on the car, I'm
not hopeful.
- I was going to buy the Bosch O2 sensor, but now I'll check for the other
brands mentioned as well
- thanks for the correction on the bank/sensor arrangments. I will test
the O2 sensor as soon as the rain lets up a bit.
--
Himanshu

First, thanks to: Richie Rich, hyundaitech, ray, lugnut, Daniel J. Stern,
Nirodac, Eric F and Jim for replying to my posts.
Luckily "Bank 2, Sensor 1" translates to the easiest O2 sensor to acces -
it's the one on the "other" cylinder bank (2,4,6), and sensor 1 is pre-cat.
So it's the one in the front of the car when you open the hood. I've
updated the pictures on the web page to show the locations of the sensors:
http://home.comcast.net/~hgohel/index.html
The wires on the O2 sensor didn't match the colors Nirodac posted - there
was no RED at all. There's a white, light blue, a dark blue and perhaps a
black or another dark blue. So I didn't know which ones to test voltages
on.
I found a few more docs on how to test the O2 sensor and one of them said I
should check continuity between two leads they showed on a harness. the
diagram didn't was for a different model year, but I poked around on the
problem sensor & found no continuity. Then I measured on those leads in two
other sensors and I did find continuity on those leads. So it seems that
this sensor may be dead.
Unfortunately none of the local stores have this sensor in-stock and I was
thinking if I would have to order it anyway, then why not try and find one
of the other sensor brands that were mentioned - NTK, NAPA, etc. But a
search on the web shows practically only Bosch brand O2 sensors...only one
site had "Walker" O2 sensors, which seemed like an off-brand. Any pointers
to vendors that have non-Bosch O2 sensors?
Thanks.
Himanshu

So today I was able to install the new O2 sensor in my Galant -
eventually I got the best price at the local Mitsu dealer, believe it
or not! It was a Denso O2 sensor Mitsubishi genuine part for $131.
That is about $35 less than the local autoparts stores for a Bosch
(which has received some negative feedback here).
Installation wasn't difficult except removal of the original O2 sensor
- man, was that a tough one to get out! I had the slotted socket
wrench but still, it was tough to get it out. The Haynes manual said
run the engine for a minute or two and that would make it easier to
remove. So I did...and eventually got it out. Ofcourse, I put some
anti-seize compound on the new one, even though there seemed to be
some on the new one anyway.
The "Service Engine Soon" light didn't go away immediately, but I will
check again tomorrow and if it's still on, I will get it reset and
watch it. However, the car does seem to be running better - idling
seems better, and the roughness in driving seems to be gone.
Finally - the old O2 sensor was completely blackened at the tip,
somewhat like the one shown under "Oil Contamination" at Bosch's site:
<http://www.boschusa.com/images/O2sensorfaces.pdf
Is there anything I should do about the oil contamination to prevent
that from happening in the future? The tip wasn't wet, just dry
black.
Thanks again.
--
Himanshu

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